This invention relates to vehicle electrical systems that use more than one operating voltage. There are a variety of means to attain multiple voltages in a vehicle, e.g. an automotive system, and one of them involves the use of an alternator that powers, among other loads, a battery equalizer. The purpose of the battery equalizer is to balance the charge among series-connected batteries to ensure equal charging. This is especially important if to one of the series-connections between the batteries represents a point where electrical loads are connected.
The charge voltage at the highest series-connected battery potential is typically controlled by a voltage regulator that controls the output voltage of the alternator. Series-connected batteries all need similar charge characteristics if they are to be equally recharged in series. If an intermediate operating voltage is derived from a series connection between batteries, the electrical loads at that point will unbalance the electrical charge that is attempting to recharge the battery at the lower potential. Also, if batteries with different charge characteristics are series connected, there will be unbalanced charging. In any type of unbalanced series charging, the battery at the higher potential will tend to overcharge, and the battery at the lower potential will tend to undercharge. In time, the overcharging battery will be destroyed, and the entire electrical system will malfunction.
An equalizer prevents battery charge imbalance because it has the capability of shunting current from the higher potential to the lower potential in order to maintain an equal potential across each of the batteries in series. However, an equalizer is a current rated device and typically has a protective circuit that prevents operating beyond its rated limit. If excessive electrical loads or a deeply discharged battery causes the operating current to exceed the equalizer rating, the equalizer may malfunction, shut down, or continue operating at its self imposed protective limit. In each of these cases the equalizer will cease to perform its equalizing function, and the higher potential battery will overcharge while the lower potential battery will undercharge.
Prior art battery charging systems that include equalizers are described in Brainard U.S. Pat. No. 5,479,083, Kutkut U.S. Pat. No. 6,150,795, Stuart U.S. Pat. No. 5,666,041, Sullivan U.S. Pat. No. 5,528,122, Nofzinger U.S. Pat. No. 4,967,136, and Sullivan U.S. Pat. No. 4,479,083.
By way of general introduction, the preferred embodiment described below seeks to overcome the limitation of the equalizer described above by introducing a voltage regulator that monitors the voltage at the series connection of series-connected batteries. The regulator is programmed to identify when an overload or malfunction occurs across any of the individual battery voltages. If this happens, the voltage regulator can adjust its regulated setting to a voltage that prevents the malfunctioning battery from overcharging. This, of necessity, may cause other batteries in the series to be undercharged, but at least it will prevent permanent overcharge damage and unsafe operation. A fault signal to alert the operator of this condition is provided. If the malfunction or overloaded condition cannot be corrected within the programmed range of output voltage adjustment, the regulator will turn off the alternator. If the overloaded condition corrects itself, the voltage regulator may return to normal operation at its original regulated setting.
This section has been provided by way of general introduction only, and it is not intended to narrow the scope of the following claims.